On Tue, Feb 27, 2024 at 10:03 PM Yafang Shao <laoar.shao@xxxxxxxxx> wrote: > > On Tue, Feb 27, 2024 at 9:20 PM Michal Hocko <mhocko@xxxxxxxx> wrote: > > > > On Tue 27-02-24 18:06:05, Yafang Shao wrote: > > > On Tue, Feb 27, 2024 at 5:45 PM Michal Hocko <mhocko@xxxxxxxx> wrote: > > [...] > > > > > Reclaiming numerous dentries through force_empty can also lead to > > > > > potential issues, which is why we attempt to shrink the slab gradually > > > > > to mitigate them. However, it's important to note that the underlying > > > > > causes of the issues in force_empty and rmdir are not identical, as > > > > > they involve different locks. > > > > > > > > Please be more specific about those issues. > > > > > > Both of these issues stem from lock contention: > > > > > > - rmdir > > > When executing rmdir, the lock of the inode of the empty directory is > > > held. If this directory contains numerous negative dentries, this lock > > > is held for an extended duration. Consequently, if other processes > > > attempt to acquire this lock, they are blocked. > > > A simple reproducer involves: > > > > > > 1. Generating numerous negative dentries in an empty directory. > > > 2. Running `rmdir ~/test` and `ls ~/` concurrently. > > > > I fail to see how is this relevant to memcg reclaim > > > It appears there might still be some misunderstanding regarding the > issue at hand. > > The numerous negative dentries are generated within a memcg. I > simplified the explanation by omitting the memcg context. > > > > > > This setup demonstrates that ls takes a significant amount of time to > > > complete due to lock contention. > > > > > > - force_empty > > > Force_empty holds the lock of super_block->dentry_list. However, I > > > haven't yet had the opportunity to produce a specific example to > > > illustrate this issue. > > > > OK, get back to us once you can identify an actual problem. We might be > > Pls. take a look at the force_empty->prune_dcache_sb->shrink_dentry_list. Please note that the spinlock is located within list_lru_walk_one. Additionally, the issue persists even with the newly introduced memory.reclaim, as it functions similarly to force_empty. > > > talking about different things here though. My question is directed at > > existing memcg interfaces to reclaim the memory. That would be legacy > > (and effectively deprecated) force_empty and memory.reclaim that we > > have. > > > > -- > Regards > Yafang -- Regards Yafang
